The present invention generally pertains to electronic communication systems and is particularly directed to the use of fiber optics in cable television (CATV) systems.
In a headend terminal of a typical CATV system, a plurality of television signals from separate television signal sources are amplitude modulated onto a plurality of carriers and then multiplexed to provide a multiplexed electrical signal. The multiplexed electrical signal is then transmitted to a distribution terminal (also known as a multi-tap or tap), from which it is further transmitted to each of a plurality of subscriber terminals over a corresponding plurality of coaxial cables that couple the distribution terminal to the plurality of subscriber terminals. Service request signals generated in the subscriber terminals typically are transmitted back to the headend terminal over telephone lines or through CATV distribution plants.
The use of optical fibers to transmit television signals in CATV systems has been suggested because of the superior long-distance transmission characteristics of optical fibers in comparison with the long-distance transmission characteristics of coaxial cable. Hightower, "Economic FO System For New Residential Services", Telephony, Mar. 17, 1986, p. 44, describes a CATV system in which the multiplexed electrical signal is converted at a central office to a multiplexed optical signal and then transmitted over a single-mode optical fiber to a multimode splitter, from which the multiplexed optical signal is distributed to a plurality of subscriber terminals over a corresponding plurality of multimode optical fibers. In the Hightower system, service request signals from the plurality of subscriber terminals are provided over separate fiber optic links to a second multimode splitter which transmits the service request signals over a multimode optical fiber to the central office. A switch used for multiplexing the signals at the central office is controlled in response to the service request signals.
The cost of such a CATV system using fiber optic links to each of the subscriber terminals is very high in comparison with the cost of a typical prior art CATV system, which uses coaxial cable links to each of the subscriber terminals.